This invention relates to a multicell battery such as used in a spacecraft power system, and, more particularly, to a controllable cell bypass system for such a battery.
A battery is formed of individual cells, each of which produces a voltage and current output. The cells are arranged in series or parallel arrays to form the battery, according to the required voltage and current output of the battery. In one practical application, the battery is used to store and provide power for a spacecraft in orbit, such as a communications satellite. Each such battery typically includes multiple cells, often as many as 20 or more cells.
The design of the battery power system of a communications satellite presents special challenges. The battery power system must continue to operate in an acceptable manner for years while physically inaccessible because the satellite is in high-earth orbit. In such multicell batteries, a bypass circuit for each of the cells is usually provided. Otherwise, if one of the cells were to fail to an open circuit condition, the battery would be rendered inoperable in the open-circuit state. The bypass circuit permits the failed cell to be bypassed, so that the battery continues to function but at a diminished performance level. It is common practice to overdesign the battery according to the statistical probabilities of failure of one or more cells in the battery, so that, through the use of the bypass circuitry, the battery can continue to function in an acceptable manner.
A number of bypass circuit designs have been utilized. For example, in one approach an individual relay is placed into each cell bypass circuit. Relays are heavy and can suffer damage during launch.
Accordingly there is a need for an improved cell bypass technique for use in spacecraft and other multicell batteries. The present invention fulfills this need, and further provides related advantages.